[scruffy]

This exists on both 4.83 and the 4.84 betas (haven't tested b6 yet):

When you save the library, the following issues occur:

1) Commas in sort name are turned to semicolons.
Example: Sort Name: Austen, Jane
Saved name in directory and files: Austen; Jane

2) All files have an exported # embedded in the title, and in the opf references to them.
Albert Einstein Quotes - Einstein; Albert_1.lit
Albert Einstein Quotes - Einstein; Albert_1.jpg
Albert Einstein Quotes - Einstein; Albert_1.opf
(The _1 is not on the originals)

This is annoying to say the least, since the # is purely a Calibre invention, and has nothing to do with the files themselves. Can you remove it?
That way, 2 exported copys of the same text/jpg/etc (perhaps from different libraries, where the # is not the same) will have identical names.

In the beta 4.84, the new library does NOT have the # on the files, but solely on the directory of the book itself. Even removing that would be a good thing, if possible...